Azithromycin is the U.S.A.N. (generic name) for 9a-aza-9a-methyl-9-deoxo-9a-homoerythromycin A, a broad spectrum antimicrobial compound derived from erythromycin A. Azithromycin is disclosed in U.S. Pat. No. 4,474,768 to Bright and U.S. Pat. No. 4,517,359 to Kobrehel et al. These patents disclose that azithromycin and certain derivatives thereof possess antibacterial properties and are accordingly useful as antibiotics.
Azithromycin is commonly administered orally, in a number of different dosage forms such as tablets, capsules, and suspensions, for the treatment of antibacterial infections. Until the present invention, however, azithromycin was not known to be effective when topically administered to the eye. Azithromycin is known to be effective for the treatment of eye infections in humans when administered systemically, e.g., orally. However, it is also known that antibiotics which are effective when administered by a systemic route are not necessarily effective when applied topically, directly to the eye. For example, it has been reported that when tetracyclines are applied to the cornea, they do not penetrate the intact normal cornea even though they are able to diffuse into spinal fluid and into ocular fluids if the systemic dose is high enough (Douvas MG, et al, Arch Opthalmol. 46:57, 1951).